Domain structure imaging by Bragg geometry X-ray ptychography
Domain structure imaging by Bragg geometry X-ray ptychography
复制标题
布拉格几何 X 射线叠层成像的域结构成像
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
R. Bean
中科院分区：
文献类型：
--
作者：
R. Bean
材料中的域结构对于其物理特性、技术用途和对外部扰动的响应非常重要。域是材料内具有一致原子结构的小区域，可能具有不同的排序起源或不同的方向。域结构存在于任何表现出相关长度短于样本范围的超结构有序性的材料中。域的大小由有序相互作用的强度和生长条件控制。域存在于从凝聚态物质到生物样品的大量材料中，并且具有针对单个样品的独特结构。对于尺寸为埃至纳米的晶体样品中的域，X 射线是一种理想的探针。许多域系统没有表现出X射线振幅对比，即所有域均匀地衰减X射线束，域结构仅在入射X射线束的相位偏差中是明显的。需要一种对这些相位差敏感的成像方法。
相干 X 射线衍射成像 (CXDI) 是一种利用样品与其在像素化探测器处收集的远场衍射图样之间的傅立叶变换关系来迭代解决相位问题并重建样品的幅度和相位图像的方法。基于支撑的相干 X 射线衍射方法通过收集反射几何中样品布拉格峰周围的散射，已成功应用于晶体结构的三维成像。一般来说，相位恢复算法的限制要求样本在 X 射线束内被隔离，因此这些方法在扩展域系统成像方面并不成功。叠层照相术是一种组合的实验和分析程序，可以通过从样品的重叠区域收集一系列衍射图案来克服对样品进行分离的要求。
本论文开发了用于布拉格几何的叠层成像算法和实验方法，目的是对扩展晶体样品中的相域结构进行成像。在讨论和详细讨论和详细介绍布拉格几何中叠印术应用的实验方法和算法之前，回顾了布拉格相干衍射成像和叠印术方法。相域结构上的叠层照相模拟以及使用专门设计的相域测试样本进行布拉格几何叠层照相 X 射线实验
证实该方法能够提供有关扩展样本域结构的准确定量相位信息。
Diamond 光束线 I16 开发了用于叠层成像的相干衍射实验装置。将布拉格叠层成像技术应用于铌薄膜中的畴结构和二元合金 Fe65Al35 中的反相畴结构的研究，并给出了重建结果。
Domain structure in materials is important for their physical properties, technological uses and response to external perturbations. Domains are small regions within a material with a consistent atomic structure that may have different ordering origins or different orientations. Domain struc¬ture is present in any material which exhibits super-structure ordering with correlation lengths shorter than the extent of the sample. The domain size is controlled by the strength of the ordering interactions and growth conditions. Domains are present in a huge range of materials from con¬densed matter to biological samples with a structure unique to the individual sample. For domains in crystalline samples with sizes of Angstroms to nanometres X-rays are an ideal probe. Many domain systems exhibit no X-ray amplitude contrast, i.e. all domains attenuate the X-ray beam uniformly, the domain structure is apparent only in the deviation of the phase of the incident X-ray beam. An imaging method is required which is sensitive to these phase differences.
Coherent X-ray Diffraction Imaging (CXDI) is a method which exploits the Fourier transform relationship between the sample and its far field diffraction pattern collected at a pixellated detector to iteratively solve the phase problem and reconstruct an amplitude and phase image of the sample. Support based coherent X-ray diffraction methods have been successfully applied to the three dimensional imaging of crystalline structures by collecting the scattering around the sample Bragg peaks in reflection geometry. In general, phase retrieval algorithm constraints require that the sample is isolated within the X-ray beam and as a result these methods have not been successful at imaging extended domain systems. Ptychography is a combined experimental and analysis procedure that can overcome the requirement for the sample to be isolated by collecting a series of diffraction patterns from overlapping regions of the sample.
This thesis develops the ptychography algorithms and experimental methods for use in Bragg geometry with the goal of imaging phase domain structures in extended crystalline samples. Bragg coherent diffraction imaging and ptychography methods are reviewed before the adaptations of the experimental method and algorithm for the application of ptychography in Bragg geometry are discussed and detailed. Simulations of ptychography on phase domain structures and a Bragg geometry ptychography X-ray experiment with a specifically designed phase domain test sample
confirm that the method is capable of providing accurate quantitative phase information on the domain structure of extended samples.
A coherent diffraction experimental setup for ptychography is developed at Diamond beamline I16. Bragg ptychography is applied to the investigation of domain structure in a niobium thin film and anti-phase domain structure in the binary alloy Fe65Al35 and the results of the reconstructions are presented.